1. Field of the Invention
The present invention relates generally to improved methods of sealing bridge plugs in pipes disposed in well bores, and more particularly, to such methods wherein the sealant is highly resilient and has high bond strength.
2. Description of the Prior Art
Mechanical bridge plugs are commonly utilized to provide isolation of a subterranean zone penetrated by a well bore having a pipe string such as casing or a liner disposed therein. For example, in perforating casing in the zone and/or in stimulation treatments performed therein after perforations have been formed, a bridge plug is set in the casing above the zone. Because bridge plugs are mechanical and rigid after being set, when a pressure differential is exerted across the plug and the casing expands as a result of the pressure, the seal between the plug and the pipe is often lost which allows the plug to be moved within the pipe by the pressure differential.
Heretofore, in attempts to prevent the loss of seal and movement of a bridge plug, a quantity of a conventional Portland cement slurry has been placed in the pipe adjacent to the bridge plug and allowed to harden. However, when the pressure differential exerted on the bridge plug and the set cement column adjacent thereto reaches a sufficient level, the ability of the cement to maintain a bond to the pipe is overcome and the entire column comprised of bridge plug and set cement is moved in the pipe. This allows fluid to flow around the plug and cement which makes the drill-out of the plug and cement extremely difficult.
Thus, there is a need for improved methods of sealing a bridge plug in a pipe whereby the sealant used hardens into a highly resilient non-permeable mass which has a high pipe surface bond strength and can withstand pipe movements and high pressure differentials without failure.